On the n810 you could hold volume down and tap for middle click or hold volume up and tap for right click. It was incredibly handy, which makes me mad that I learned about it only a week or two before my n900 showed up...
As far as I know there's not a good way to right click at this point because the volume keys are intercepted for volume control.
I just tried this on the latest N900 vncviewer and it works! Hold volume up when clicking does indeed send a right click command!
I was reading another post about something different when someone suggested using the proximity sensor as a way to detect alternate clicks; Have to say, that might be an even better idea, as if you hold the n900 with your left hand you can easily cover up the prox sensor to do an alternate click motion (I can only ever recall X windows being big on middle click for pasting, did Windows ever use it?)
It should be possible for the developer to remap the volume buttons to provide this functionality, as the latest FBReader builds for the N900 use the volume buttons for page up/page down. I would REALLY like to see this functionality in VNC and Remote Desktop.
